A circuit board in general is a flat non-conductive board on which dozens or hundreds of minaturized electrical components are mounted. Electrical conductors are laid down in a predetermined pattern between the components and the end product is used to control the electronic function of a machine or the like.
Circuit boards are produced by the hundreds of thousands. It is quite essential that they be produced through automation and typically a series of automated operations are employeed to produce the boards. In order to coordinate these operations, it is important that the boards be produced to exactly a specified size, that the boards be mounted exactly at a designated position within each work station, e.g. in a drilling operation, that the holes (in which the components are mounted) be drilled exactly in the right place on the board and relative to each other, etc., etc. The tolerances that have to be met are measured in the thousandths of an inch and these tolerances get tighter and tighter as the circuitry demanded of the circuit boards gets more complex.
Because circuit boards are moved from one station to another, there must be a means for determining that each station uses the same reference point. Thus, it is common to equip the boards with locating pins. A pair of locating pins are precisely mounted to each board and each station includes apertures precisely located within the station wherein these pins are inserted. The equipment with proper programing can thus determine the precise location of every position on the board. The tooling plate of the numerically controlled drill (CNC drill) for one, has to be fitted with these apertures.
Heretofore the tooling plates of the CNC drill were ordered from the plate manufacturer with the locating apertures to be drilled into the plate to e.g., plus or minus 0.001 inch. The plates are very expensive to produce because of the accuracy required for locating the locating apertures. Furthermore, even when produced within the specifications, variance is generated due to temperature differences. That is, unless the CNC drill is operated at the same temperature that existed when the plates were made, the plate's thermal expansion properties will cause some distortion and offset the aperture location.